The present invention relates to a three stage switching apparatus and, more particularly, to a network of a three stage switching apparatus and its structure.
Three stage switching networks are often used as switching networks having N input terminals and N output terminals and freely connecting the input and output terminals. An example of a three stage switching network is described in "A Study of Non-Blocking Switching Networks" on BELL SYSTEM TECHNICAL JOURNAL Vol. 32, No. 2, pp. 406 to 424. As described in this paper, a switching network can be conveniently applied to a large telephone switching system since the larger the number N of input/output terminals, the smaller the number of crosspoints than N.sup.2.
However, in the conventional three stage switching networks, redundancy is not considered. Therefore, even when a single switch is failed, one of the most important functions of a switching network to connect arbitrary input and output terminals is lost.
In a conventional switching system having a three stage switching network, since printed circuit boards constituting the respective stages are connected to each other through a back wired board, the number of signal lines is limited and the wiring is complex.